1. Field of the Invention
The present invention relates to a wavelength-multiplexed optical transmission system in which optical signals having different wavelengths are multiplexed and transmitted, and more particularly to an optical transmission device applicable to such a system.
A wavelength-multiplexed optical transmission system is known as a large-capacity transmission system. The wavelength-multiplexed optical transmission system includes terminal equipment or devices receiving and transmitting optical signals, optical cross-connect devices, add/drop devices and optical amplifiers. The optical cross-connect devices perform an add and drop operation on an optical signal and a wavelength interchanging operation. The wavelength-multiplexed transmission system is required to avoid collision of optical signals having the same wavelength and to manage wavelengths used.
2. Description of the Related Art
FIG. 1 schematically illustrates a wavelength-multiplexed optical transmission system.
The system includes terminal devices 201 and 202, an optical cross-connect device 203, an optical amplifier 204, and optical transmission paths 205. The terminal devices 201 and 202 multiplex optical signals of wavelengths xcex1-xcexn, and transmit and receive multiplexed optical signals. The optical cross-connect device 203 is equipped with the functions of setting cross-connects from incoming paths to outgoing paths and performing the add/drop operation on the optical signals. The function of setting the cross-connects include a wavelength conversion of optical signals. The cross-connect device 203 can add or drop an optical signal having a wavelengthxcexx. Although only one optical cross-connect device 203 is illustrated in FIG. 1, a plurality of optical cross-connect devices can be connected in accordance with the size of the network. An ADM (Add/Drop Module) may be used in which an optical filter is utilized to drop and add optical signals.
The optical amplifier 204 is provided in the optical cross-connect device 203 or in a repeater provided in the optical transmission paths 205 at given intervals. The optical amplifier 204 amplifies the wavelength-multiplexed optical signal as per se. For example, the optical amplifier 204 employs a rare-earth doped optical fiber, which receives a received optical signal and an exciting (pumping) light, so that the received optical signal can be amplified. The level of the amplified optical output signal can be controlled by controlling the power of the exciting light.
Generally, the optical amplifier 205 is controlled by an automatic level control (ALC) so as to obtain a constant optical output level. The automatic level control controls a current that flows in a semiconductor laser generating the exciting light. If the optical signal having a certain wavelength contained in the wavelength-multiplexed optical signal is broken, the optical signals of wavelengths other than the above certain wavelength are excessively amplified in order to obtain the constant optical output level. Hence, there is an increased possibility that the interference between the wavelengths may be increased or error in receipt due to level variations in the respective wavelengths on the receive side may be increased. In contrast, when an increased number of wavelengths is used, the levels for the wavelengths that are already used are decreased in order to maintain the optical output level at constant.
With the above in mind, the wavelength-multiplexed optical signal is demultiplexed into the respective optical signals, and monitors such as photodiodes are provided to the respective wavelengths. The monitors are used to determine whether the respective wavelengths are now in use. Hence, it is possible to determine whether each of the optical signals having the respective wavelengths has been broken down. Further, it is possible to detect a situation in which an optical signal of another wavelength is started to be used. The number of wavelengths that are in use can be obtained and thus the automatic level control of the optical amplifier 205 can be performed based on the number of wavelengths that are in use.
The optical signals are modulated by using frequencies respectively provided to the wavelengths thereof, and are multiplexed before transmission. The optical amplifier 205 is equipped with a monitor converting an optical signal into an electric signal, and filters respectively provided to the modulation frequencies. The optical signals are detected by the filters in order to detect the breakdown of an optical signal and an event in which an optical signal is started-to be used. Hence, the automatic level control of the optical amplifier 205 can be performed based on the number of wavelengths that are in use.
When the system is started to operate, the terminal devices 201 and 202 inform the optical amplifier 205 of the number of wavelengths to be used by means of control information. The optical amplifier 205 performs the automatic level control based on the number of wavelengths to be used. A method has been proposed in which if there is a wavelength which is started to be used or stopped while the system is working, the optical amplifier 205 is informed of the presence of the above wavelength by the control information. Hence, the optical amplifier 205 receives the control information and performs the automatic level control based on a change of the number of wavelengths.
However, the prior art described above has the following disadvantages. In the case where the optical amplifier 205 employs the automatic level control using the monitors for the respective wavelengths, as an increased number of wavelengths is used, the optical amplifier 205 has an increased circuit size. This increases the cost. In the case where the optical amplifier 205 employs the filters, only one monitor is required to convert the optical signal into the electric signal. However, the optical amplifier 205 requires the filters equal in number to the frequencies for modulation. This increases the circuit size and the production cost.
The arrangement is less expensive in which the terminal devices 201 and 202 inform the optical amplifier 205 of the number of wavelengths to be used by the control information. However, the optical amplifier 205 is required to have the functions of receiving and discriminating the control information, identifying the wavelengths that are in use by means of software, and performing the automatic level control based on the number of wavelengths that are in use. However, a considerable long time is required to execute the software process. Further, it is difficult to automatically change the levels at the same time as the number of wavelengths is changed. Hence, the level of the received level may instantaneously be increased or decreased. Such an abrupt change in the level of the optical signal may increasingly cause a burst error on the reception side.
In the wavelength-multiplexed optical transmission system including the optical cross-connect device 203, a plurality of terminal devices are mutually connected via the cross-connect device 203. Hence, it is difficult to inform all the optical amplifiers 205 of the number of wavelengths that are in use. Particularly, the arrangement of the optical cross-connect devices 203 performing the wavelength change and route switching makes it possible to ensure the stable automatic level control of the optical amplifiers 205. If the wavelength-multiplexed optical transmission system has an increased scale and a complex configuration, different terminal devices may use optical signals of the same wavelength. In such a case, the optical signals collide with each other, and the normal transmission is no longer ensured.
In the wavelength-multiplexed optical transmission system having a plurality of terminal devices, optical signals of the same wavelength may collide with each other in the optical cross-connect device or the like. In order to avoid the above collision, all the terminal devices are asked to determine whether a newly used wavelength collides with the existing optical signals. As the system size is increased, it is very difficult to search for an available wavelength.
It is a general object of the present invention to provide an optical transmission device suitable for a wavelength-multiplexed optical transmission system in which the above disadvantages are eliminated.
A more specific object of the present invention is to easily manage and notify of information concerning the wavelengths which are used and to easily control optical amplifiers and search for transmission routes.
The above objects of the present invention are achieved by An optical transmission device that can be applied to a wavelength-multiplexed optical transmission system, the optical transmission device comprising: a first part creating a supervisory control signal to be transmitted in optical formation together with an optical main signal, the supervisory control signal comprising a vector of elements respectively corresponding to wavelengths; and a second part converting a vector included in a supervisory control signal received from a remote optical transmission device into another vector by a process using a path matrix in the vector received forms diagonal elements of the path matrix, the above another vector being transmitted to a next stage in the wavelength-multiplexed optical transmission system.
The optical transmission device may further comprise a third part which transmits a wavelength information vector indicating that the number of wavelengths used is zero to a next stage in the wavelength-multiplexed optical transmission system, when the supervisory control signal and the main signal are broken down.
The optical transmission device may be configured so that: the vector is a wavelength information vector which indicates the number of wavelengths used in the main signal; and at least one of the optical transmission devices comprises a third part which determines whether there is a collision of wavelengths used by referring to wavelength information vectors received from a plurality of routes.
The optical transmission device may further comprise a third part which returns the supervisory control signal including a received-state vector indicating wavelengths which are normally received to a transmission side which transmits the vector created by the first part.
The optical transmission device may further comprise a third part which returns, to a transmission side which transmits the vector created by the first part, when receipt of an optical signal from any one of routes to which an optical signal of an identical wavelength branches is confirmed, the supervisory control signal including a received-state vector formed by performing an OR operation on received-state vectors received from the routes.
The optical transmission device may further comprise a third part which returns, to a transmission side which transmits the vector created by the first part, when receipt of optical signals from all routes to which an optical signal of an identical wavelength branches is confirmed, the supervisory control signal including a received-state vector formed by performing an AND operation on received-state vectors received from the routes.
The optical transmission device may further comprise a third part which comparing the vector serving as a wavelength information vector indicating wavelengths used with a received-state vector indicating wavelengths normally received and identifying a fault from a mismatch between corresponding elements in the wavelength information vector and the received-stage vector.
The optical transmission device may further comprise an optical transmission device which transmits a wavelength retrieving vector for retrieving a wavelength usable by using the supervisory control signal and returns a retrieval result indicating a retrieved usable wavelength and a device ID by using the supervisory control signal.
The optical transmission device may be configured so that the optical transmission devices transmits a wavelength retrieving vector for retrieving a wavelength usable by using the supervisory control signal and returns a retrieval result indicating a retrieved usable wavelength, a device ID and a counter value indicating an order of receipt of the wavelength retrieving vector by using the supervisory control signal.
The optical transmission device may further comprise a receiving direction memory part which stores a direction in which a wavelength retrieving vector indicating a usable wavelength is received, and a direction in which a response is received, the response being sent in receipt of a newly created wavelength information vector from the wavelength retrieving vector and the wavelength information vector which vectors are received.
The optical transmission device may further comprise: a receiving direction memory part which stores a direction in which a wavelength retrieving vector indicating a usable wavelength is received, and a direction in which a response is received, the response being sent in receipt of a newly created wavelength information vector from the wavelength retrieving vector and the wavelength information vector which vectors are received; and a part which resets the receiving direction memory part after the optical transmission device is controlled to use the usable wavelength in accordance with a route switching instruction.
The optical transmission device may further comprise a third part which sends, by the supervisory control signal, a wavelength retrieving vector for retrieving a usable wavelength, and a route switching instruction indicating whether the usable wavelength should be used by switching.
The optical transmission device may further comprise a third part which performs setting of a network side or a terminal side on the basis of a magnitude of a value of a device ID of an opposing optical transmission device at the time of establishing a data link for sending and receiving the supervisory optical transmission signal.
Another object of the present invention is to provide an optical amplifier which can be applied to a wavelength-multiplexed optical transmission system having an optical transmission device comprising: a first part creating a supervisory control signal to be transmitted in optical formation together with an optical main signal, the supervisory control signal comprising a vector of elements respectively corresponding to wavelengths; and a second part converting a vector included in a supervisory control signal received from a remote optical transmission device into another vector by a process using a path matrix in the vector received forms diagonal elements of the path matrix, the above another vector being transmitted to a next stage in the wavelength-multiplexed optical transmission system, the optical transmission, the optical amplifier comprises: a first part which directly amplifies the optical signal; the vector included in the supervisory control signal is a wavelength information vector indicating wavelengths used in the main signal; and the optical amplifier performs an automatic level control based on the number of wavelengths indicated by the wavelength information vector.
The optical amplifier may be configured so that the optical amplifier performs the automatic level control so that, when only the supervisory control signal is broken down, the automatic level control is based on a number of wavelengths used immediately before the supervisory control signal is broken down.
The optical amplifier may be configured so that the optical amplifier performs the automatic level control so that, when the supervisory control signal and the main signal are broken down, the automatic level control is based on a condition in which the number of wavelengths used in the main signal is equal to zero.
The optical amplifier may be configured so that it comprises a part which gradually controls an output level based on an increase or decrease in the number of wavelengths used in response to a notification indicating such an increase or decrease and returns the output level to an original level based on the number of wavelengths used before the increase or decrease when a fault occurs while gradually controlling the output level and the optical amplifier is notified of the fault by the supervisory control signal.
A further object of the present invention is to provide a wavelength-multiplexed optical transmission system comprising: a plurality of optical transmission devices, each of the optical transmission devices comprising: a first part creating a supervisory control signal to be transmitted in optical formation together with an optical main signal, the supervisory control signal comprising a vector of elements respectively corresponding to wavelengths; and a second part converting a vector included in a supervisory control signal received from a remote optical transmission device into another vector by a process using a path matrix in the vector received forms diagonal elements of the path matrix, the above another vector being transmitted to a next stage in the wavelength-multiplexed optical transmission system.
The wavelength-multiplexed optical transmission system may be configured so that: one of the optical transmission devices serves as a master station, and remaining optical transmission devices serve as slave stations; a path retrieval or a route retrieval using the wavelength retrieving vector is carried out by the master station or one of the slave stations which is allowed to perform the path retrieval or the route retrieval by the master station; and one of the slave stations is set to a new master station if a fault occurs in the master station.